STUDY OF THE REASONS THAT INDUCE CRACKS AT BRIDGE DECK END

Transcription

1 STUDY OF THE REASONS THAT INDUCE CRACKS AT BRIDGE DECK END by Zhengyu Liu Research Team: Zhengyu Liu, Graduate Research Student, Bridge Engineering Center, Iowa State University Brent M Phares, Director, Bridge Engineering Center, Iowa State University Lowell F. Greimann, Bridge Engineering Specialist, Bridge Engineering Center, Iowa State University Mike Nop, Bridge Engineer, Iowa Department of Transportation Ahmad Abu-Hawash, Bridge Engineer, Iowa Department of Transportation

2 OUTLINE 1. Background 2. Literature Review 3. Objective 4. Field Testing 5. Finite Element Model (FEM) 6. Parametric Study 7. Conclusion

3 Joints on Bridge Deck Snow, water and debris BACKGROUND Deterioration of deck & girder Continuous Bridge Deck: Slow down corrosion Diagonal Cracks Reduce maintenance cost Problem: Cracks in the deck Longitudinal Cracks NO agreement on bridge widths

4 LITERATURE REVIEW Longitudinal cracks are not due to concrete shrinkage Restrained shrinkage cracks are unavoidable. Bridge with large skew have higher deck strain. Stringer D. J. and Burgueño R. (2012). Identification of Causes and Solution Strategies for Deck Cracking in Jointless Bridges. Report No. RC-1571, Final report to Michigan Department of Transportation, Michigan State University, Lansing, Michigan.

5 OBJECTIVE Objectives: Study behaviors and structural characteristics that result in cracks at the deck ends with the goal of making recommendations regarding geometric constraints specifically bridge width limitations To Achieve these Objectives: Field testing Finite element model development and calibration Parametric study

6 FIELD TESTING Live-load testing Long-term testing

7 FIELD TESTING Bridge Selection: Bridge # Crack pattern Traffic condition Side view Safety ft.; four span; 1.5 skew; Integral abutment; 12 pre-stressed concrete girders Cross-sectional view

8 Live-load Testing: Instrumentation plan FIELD TESTING Top view Cross-sectional view

9 FIELD TESTING Live-load Testing: Five load cases Load cases G11

10 FIELD TESTING 40 Live-load Testing: Results are symmetric Bridge is stiff Top flange strain is small; neutral axis is near the girder/deck interface Microstrain Middle Abut Pier Front Axle Position (ft) Load case1- Girder 11- Bottom flange gauges

11 FIELD TESTING Long-term Testing: (Instrumentation plan) Strain at the bottom of deck Temperature at the abutment, bottom of deck and mid-depth of deck Displacement in both longitudinal and transverse direction

12 Long-term Testing: (Results) FIELD TESTING am 12/4/ am 12/5/ am 12/29/ am 12/30/ am 2/11/ am 2/12/ am 3/10/ am 3/11/ ( F) Uniform temperature change at deck -150 Strain data at 4 th bay, Near abutment Abutment temperature change = 2/3 deck temperature change Strain data and displacement data change with temperature change

13 Finite Element Model (FEM) Development of model Calibration for live-load behavior Validation from long-term behavior Validation from crack pattern

14 Finite Element Model (FEM) Development of Model: ANSYS Shell 181 & Beam 4 Element size 6in Pile/pier columns not included Smear of steel

15 Calibration for Live-load Behavior: Finite Element Model (FEM) Girders are stiffer than as designed due to high concrete strength/stiffness 10 5 Field Testing Original E 10 5 Increased E Microstrain Front Axle Position (ft) FEM Microstrain Front Axle Position (ft)

16 Finite Element Model (FEM) Validation from Long-term Behavior: Loading Temperature difference Temperature gradient Conclusion FEM is valid Temperature loading 250 Field Testing Data FEM ( F) Strain data at 4 th bay,

17 Finite Element Model (FEM) Validation from Crack Pattern: Annual temperature change Abutment temperature change = 2/3 deck temperature change Temperature gradient through abutment thickness and height Annual temperature change

18 Finite Element Model (FEM) Validation from Crack Pattern: Annual temperature change can crack model Model is valid Results shown

19 PARAMETRIC STUDY Parameter Study Case Conclusions Deck width 40ft; 90ft; 160ft Minimal effect Bridge skew 0-degree; 45-degree Minimal effect Abutment type integral; stub Lower strain with stub abutment Girder spacing 88in.;176in. Minimal effect Pier type expansion; fixed Minimal effect No. of spans one; three Minimal effect Girder type steel; concrete Minimal effect

20 Bridge Width PARAMETRIC STUDY

21 PARAMETRIC STUDY Bridge Skew a. 0-degree bridge b. 45-degree bridge

22 PARAMETRIC STUDY Abutment Type Integral abutment Stub abutment

23 CASE STUDY Bridge #608585: 220 ft. long Three span 36 degree skew Two abutment types Deck top crack pattern Stub Abutment Integral Abutment

24 CONCLUSIONS AND RECOMMENDATION Strain/crack: ΔT and restraints Integral abutment bridges: more crack prone Stub abutment bridges: less crack prone Other parameters: minimal/no influence Including bridge width recommend that bridge width limitations can be increased

25